Seasonal affective disorder 'may be a myth', study argues

"Stop blaming SAD for your bad mood - it doesn't exist! Seasonal changes have 'NO effect on depression'," the Daily Mail reports. A new study found no significant association between lack of sunshine and reported symptoms of depression…

Seasonal affective disorder (SAD) is described as a type of seasonal depression that may partly be triggered by reduced exposure to sunlight. This, in turn, can affect mood in a number of ways.

In this study, researchers took data from a telephone survey of around 35,000 people to see if season, latitude and sunlight exposure had a significant association with reported symptoms of depression. They did not find an association.

So does this mean SAD is a "myth", as some headlines claim? Not necessarily. A telephone survey is a very blunt tool and is no substitute for a face-to-face diagnosis by a trained clinician.

There is also, to some extent, a stigma attached to mental health problems, meaning some participants may not have provided entirely truthful answers.

The important thing is if you are feeling depressed, whatever the time of year, seek medical advice from your GP.

SAD can be treated in the same way as depression, with talking therapies and medication. Some people have also reported benefiting from light box therapy, though the weight of evidence supporting this is relatively limited.

Where did the story come from?

The study was carried out by researchers from Auburn University at Montgomery. No funding source or conflicts of interest were reported.

It was published in the peer-reviewed journal Clinical Psychological Science.

As is often the case, a single dissenting opinion has been overstated in the media as a change in expert consensus opinion.

SAD is recognised by bodies such as the Royal College of Psychiatrists and is included as a diagnosis in the American Psychiatric manual DSM-5.

Causes are likely to be multifactorial, rather than the oversimplification that the condition is caused by a reduction in sunlight exposure.

What kind of research was this?

This was a cross-sectional study investigating SAD and whether there is a genuine link between exposure to sunlight and depressive symptoms. A number of analyses were conducted to assess this.

This type of study is not able to prove or disprove cause and effect.

What did the research involve?

The researchers administered the Behavioural Risk Factor Surveillance System telephone survey to a random selection of the population in the United States.

The findings were analysed in a number of ways to draw links between sunlight exposure and depressive symptoms, including:

relationship of season

latitude or season

sunlight exposure

All models also assessed the effect of the following confounding variables:

age

race/ethnicity

gender

educational level

marital status

employment status

Classification of depression was made using an adaptation of the Patient Health Questionnaire depression scale (PHQ-8), a validated tool used to screen for symptoms of depression and give a rough guide to severity. The question about suicide was removed.

What were the basic results?

The researchers analysed the surveys of 34,294 people with an average age of 52 years. There were 1,754 participants who were depressed, according to the PHQ-8 depression scale.

The researchers conducted their statistical models and found no effect of season, latitude or sunlight exposure on reported symptoms of depression.

How did the researchers interpret the results?

The researchers concluded that, "Depression was unrelated to latitude, season, or sunlight. Results do not support the validity of a seasonal modifier in major depression.

"The idea of seasonal depression may be strongly rooted in folk psychology, but it is not supported by objective data. Consideration should be given to discontinuing seasonal variation as a diagnostic modifier of major depression."

Conclusion

This cross-sectional study investigated whether season, latitude and sunlight exposure are linked to depressive symptoms that can be experienced in SAD.

The researchers found these factors had no effect on the occurrence of depressive symptoms.

However, this study has a number of important limitations. Depression was not a clinical diagnosis – it was based on the participant's response to a questionnaire over the phone.

This presents problems, as some people may not have answered questions truthfully, and those with depression or SAD may not have answered the phone.

The Royal College of Psychiatrists says around 3% of people will experience significant winter depression. This can be managed in the same way as clinical depression, through self-help techniques, talking therapies, medication, and the use of light box treatments.